Binary search to find the range in which the number lies

Question

I have an array

Values array: 12 20 32 40 52
              ^  ^  ^  ^  ^
              0  1  2  3  4

on which I have to perform binary sear

Answer 1

A regular binary search on success returns the index of the key. On failure to find the key it always stops at the index of the lowest key greater than the key we are searching. I guess following modified binary search algorithm will work.

Given sorted array A
Find a key using binary search and get an index. 
If A[index] == key
    return index;
else 
   while(index > 1 && A[index] == A[index -1]) index = index -1;
   return index;